Clean up art::HConstant predicates.

- Make the difference between arithmetic zero and zero-bit
  pattern non ambiguous.
- Introduce Boolean predicates in art::HIntConstant for when
  they are used as Booleans.
- Introduce aritmetic positive and negative zero predicates
  for floating-point constants.

Bug: 27639313
Change-Id: Ia04ecc6f6aa7450136028c5362ed429760c883bd
diff --git a/compiler/optimizing/code_generator_arm64.h b/compiler/optimizing/code_generator_arm64.h
index 10f1e7f..0af825b 100644
--- a/compiler/optimizing/code_generator_arm64.h
+++ b/compiler/optimizing/code_generator_arm64.h
@@ -257,6 +257,9 @@
                                vixl::Register obj,
                                uint32_t offset);
 
+  // Generate a floating-point comparison.
+  void GenerateFcmp(HInstruction* instruction);
+
   void HandleShift(HBinaryOperation* instr);
   void GenerateImplicitNullCheck(HNullCheck* instruction);
   void GenerateExplicitNullCheck(HNullCheck* instruction);